Doppler blood flow velocimetry of the fetal pulmonary arteries with determination of the acceleration time to ejection time ratio (AT/ET) can predict pulmonary hypoplasia in the fetus. This can help identify those infants who may experience severe respiratory failure after delivery. The authors are from Osaka University and Rinku General Medical Center.


The Doppler waveform of blood flow through the normal fetal pulmonary artery shows a "spike and dome" pattern, with a short, sharp rise during the acceleration phase followed by a dome-shaped period of decreasing flow.


acceleration time to ejection time ratio (AT/ET) =

= (time from onset to peak blood flow in milliseconds) / (time from onset to end of systolic blood flow in milliseconds)



• The time form onset to peak flow goes from minimal to maximal flow (top of spike).

• The values do not appreciably change from 20 to 30 weeks of gestation.

• The presence of congenital malformations or technical difficulties may limit the examination to only one pulmonary artery.


Pulmonary Artery

mean AT/ET ratio

mean AT/ET ratio - 2 standard deviations








Pulmonary hypoplasia was associated with:

(1) a low AT/ET ratio in both pulmonary arteries (if both obtainable)

(2) a low AT/ET ratio in one pulmonary artery (if only 1 side obtainable)


All infants with a normal AT/ET ratio in the pulmonary artery from at least one side survived.



• The initial data showed a positive and negative predictive value of 100% respectively. This was conducted in 160 normal fetuses and 17 fetuses with congenital anomalies.


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